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Scientists uncover a city, a chamber, and a complex, and map a tunnel network.

Scientists uncover salt chambers, bunkers, old kingdoms, and mysterious caves.

Investigate a tomb in Naples that may contain a prince who inspired the legend of Dracula. Read the desperate letters of Jewish rebels hidden in an Israeli cave, tour a 6,000-year-old labyrinth in Malta, and see the oldest human burial in Africa.

Crawl through a notorious brick-lined tunnel system in a historic Florida neighborhood. Open a window into the lives of elite Greek families in Naples, explore a three-story underground city in Iran, and find 2nd-century barracks buried in Rome.

Explore a labyrinth built beneath Washington, D.C., by an eccentric entomologist. Admire a fresco-filled Roman mausoleum, spot intricate chambers carved into Colombia's volcanic rock, and see a sprawling network of hand-dug tunnels in Liverpool.

Walk the service tunnels hidden beneath Emperor Hadrian's lavish villa in Italy. Uncover a chilling mass grave from the Thirty Years' War in Germany, find the foundations of a Roman basilica in London, and glimpse Neolithic life on a Danish island.

Examine a Revolutionary War-era ship found in the rubble of the World Trade Center. Uncover a mass grave of Viking settlers in Oxford, visit the resistance bunkers of the Warsaw Ghetto Uprising, and tour a necropolis full of burial jars in Corsica.

Dig beneath the Treasury in Petra, Jordan, to find a sealed tomb containing 12 skeletons; unearth a hoard of coins hidden during a Scottish massacre, question the purpose of an empty grave in Peru, and inspect a Bronze Age leader's coffin in England.

Discover a massive underground chamber hiding under the Seoul subway. Visit a medieval knight's limestone tomb in Poland, examine Roman ruins beneath a church in England, and ponder the identity of a 10-million-year-old fossil in Los Angeles.

Visit a strange wood-lined tunnel beneath a Copenhagen train station. Locate one of North America's earliest schools for Black children in Virginia, excavate a warrior cemetery in Finland, and unearth a women-only burial plot beneath a Welsh castle.